1. Field of the Invention
This invention relates to a measuring apparatus for continuously measuring fine particles, particularly the particles of soot contained in the exhaust gas emitted from diesel engines.
2. Description of the Prior Art
It is known that the fine particles in the exhaust gas of diesel engines are of two general types:
(1) White smoke or blue smoke which is a precursor of soot (an exhaust consisting of concentrated hydrocarbon drops and lubricating oil) which is called s.o.f. (soluble organic fraction) and which is soluble in an organic solvent, and PA0 (2) Soot particles known as "dry soot", which is insoluble in an organic solvent.
Soot is not only unpleasant to see spewing out of the exhaust pipes of diesel vehicles, it is also unhealthy and dirty and is subject to U.S. environmental emission regulations. In the United States, the standard method of measuring soot concentrations in vehicle emissions recognized by the U.S. Environmental Protection Agency, which is responsible for promulgating and enforcing emission regulations, is based on the measurement of the weight of soot particles captured by a filter placed in the exhaust passage for a fixed period of time.
However, with this method of weighing the soot particles trapped by a filter, data cannot be collected on a continuous basis in the course of various trials during attempts to achieve improvements in the reduction of soot particles. In this regard, the makers of diesel vehicles have sought the development of a continuously measuring apparatus, by the operation of which it becomes feasible to determine on a real time basis the rate of emission of soot particles.
Prior devices for measuring the rate of emission of particulate matter continuously, such as devices which carry out the light scattering method and the opto-acoustic method by a CO.sub.2 -laser, however, are sensitive not only to the soot particles, but also to the s.o.f. These devices therefore are not able to accurately measure the rate of emissions of soot particles only.